1. Field of the Invention
The present invention relates to a water-based ink for ink-jet recording, an ink cartridge, and an ink-jet recording method.
2. Description of the Related Art
In a water-based ink for ink-jet recording, a self-dispersible pigment is used in some cases. The self-dispersible pigment can be obtained by performing a treatment such that at least one hydrophilic group such as phosphate group, carboxylic group, or sulfonate group (sulfonic acid group), or a salt thereof is bonded to the pigment. Since the self-dispersible pigment does not require any polymeric pigment dispersant, the self-dispersible pigment is capable of preventing the viscosity of the water-based ink from increasing. Further, a self-dispersible pigment, among the hydrophilic groups each bonded to the pigment, which is treated in particular with the phosphate group can obtain high optical density (OD value) as compared with a self-dispersible pigment which is treated with the carboxylic group or the sulfonate group.
On the other hand, the water-based ink using the self-dispersible pigment treated with the phosphate group has a problem such that the ink composition thereof generally does not have satisfactory re-dispersion property. In a case that the water-based ink which does not have the satisfactory re-dispersion property is once evaporated to dryness with resultant solid matter in the vicinity of an, ink channel and/or nozzles of an ink-jet head, the following situation may possibly arise. That is, in a case that the water-based ink is tried to be jetted again and that the solid matter is newly brought in contact with the water-based ink, the solid matter is not dissolved and dispersed. Thus, it is feared that any trouble occurs in jetting stability.
Accordingly, improvement in the re-dispersion property is required in the water-based ink using the self-dispersible pigment treated with the phosphate group. In addition, although the water-based ink for ink-jet recording using the self-dispersible pigment treated with the phosphate group can obtain high optical density (OD value) as compared with the self-dispersible pigment which is treated with the carboxylic group or the sulfonate group, further improvement in the optical density (OD value) is required in the water-based ink using the self-dispersible pigment treated with the phosphate group.
In view of the above situation, an object of the present teaching is to provide a water-based ink for ink-jet recording which includes a self-dispersible pigment, which has excellent re-dispersion property, and which can obtain high optical density (OD value).